Reciprocating-piston pumps which are driven by a magnet are known, for example, from documents DE 43 28 621 C2, DE 102 27 659 B4, DE 10 2006 019 584 B4 or DE 10 2008 010 073 B4. Said pumps are used as a rule as metering or delivery pumps and serve to deliver a proportional conveying flow depending on the frequency of the electric actuation.
Furthermore, units which are called a metering pump or linearly driven pumps are known, for example, from property rights DE 40 35 835 A1, DE 10 2008 013 441 B4 or DE 298 21 022 U1.
DE 35 04 789 A1 describes a reciprocating-piston pump having an electromagnetic drive, in which an armature with a piston, which is connected thereto and configured as a piston rod, is moved away from an outlet on account of the excitation of a coil. The pump also includes a restoring spring which is supported against the armature and a spring abutment being stressed during the movement away from the outlet. When the coil is de-energized, the restoring spring moves the actuator which is formed from the armature and piston rod against an outlet stop which forms an adjustable end stop for the actuator within the housing of the pump. The pump has a suction-side first displacement space which is called a suction space and a second displacement space which is called an armature space, which displacement spaces are connected to one another by a fluid-conducting channel and a nonreturn valve provided therein and radial holes in such a way that a preferred flow from the first to the second displacement space is made possible. Here, a further nonreturn valve is arranged in a transition region between an inlet and the first displacement space. Here, the restoring spring has a prestress which is sufficient to displace the actuator against the outlet upon de-energization and to eject the entire volume of the second displacement space. In addition, the active force of the restoring spring is further reinforced by virtue of the fact that the inlet-side end face of the piston which faces the first displacement space is loaded with fluid there and is therefore pressed in the direction of the outlet. Although the prestress of the restoring spring can also be increased by way of the setting of the position of the outlet stop, its force is already far higher than a counterforce which results from the setpoint value of the pressure and cross section of the outlet face, with the result that no adaptation to the setpoint value of the pressure in the outlet is possible in this way.